Drop on demand ink-jet technology is widely used in the printing industry. Printers using drop on demand ink-jet technology may use a plurality (i.e. an array) of electrostatic actuators, piezoelectric actuators, or thermal actuators to eject ink from a plurality of nozzles in an aperture plate (nozzle plate). Even though they are more expensive to manufacture than thermal ink jets, piezoelectric ink jets are generally favored, for example, because they can use a wider variety of inks.
Piezoelectric ink-jet printheads include an array of actuators (i.e. piezoelectric elements or transducers), which are selectively operated to eject ink onto a print medium to form a printed image. Piezoelectric ink-jet printheads generally also include a flexible diaphragm to which the array of piezoelectric elements is bonded, and an adjacent body chamber or ink chamber. The diaphragm may be a metal layer that functions as a lower electrode that is common to a plurality of actuators, or a non-metal layer coated with a metal layer that provides an individual, electrically conductive lower electrode for each actuator. When a voltage is applied across one of the actuators, the actuator bends or deflects, causing the diaphragm to flex, which may either fill the body chamber with ink or eject a quantity of ink from the chamber through a nozzle, depending on the polarity of the electrical signal.
Generally, each actuator is aligned with each body chamber and nozzle. Thus, one method of improving the printing resolution of an ink-jet printer employing piezoelectric ink-jet technology is by increasing the density of the actuators and their corresponding nozzles.
However, forming ink-jet printheads becomes increasingly more difficult with decreasing actuator sizes and thicknesses. While microelectronic fabrication of printhead structures would provide precise control of the resulting structures, such methods are volume sensitive and capital intensive, which may preclude their use for low volume or custom products.
Alternatively, current piezoelectric ink jet printheads may use a bulk piezo transducer material, such as lead zirconate titanate (PZT) system that is between 50 μm and 100 μm thick, bonded to stainless steel diaphragms that are between 20 μm and 40 μm thick and square or parallelogram body chambers with dimensions on the order of 400 to 800 μm per side. Such bulk piezo material is typically pre-cut and then bonded to the diaphragm using an epoxy process. Many current printheads use the lead-containing PZT material, which is non-green but is currently permitted by the Restriction of Hazardous Substances Directive under exemptions that will eventually expire. Thus, lead-free piezo materials for printhead applications are desirable.
One lead-free bulk actuator material alternative to PZT is a bismuth sodium potassium titanate (BNKT) based material system. When operated at high electric fields, a BNKT-based lead-free piezo material can give good actuator performance.
However, in order to produce such high electric fields using reasonable voltage levels (less than 100 to 120 volts peak-to-peak), the material must be significantly thinner than is currently used. Moreover, the BNKT-based lead-free actuator materials that are thin enough to be used in printheads are also too thin and fragile to be manufactured and handled in a free-standing state, then diced and bonded using existing methods.
Thus, new lead-free piezoelectric printheads and methods for making such printheads are desirable.